The present invention relates to a showerhead for applying gas in the process chamber of a process apparatus designed to perform a specific process on objects such as semiconductor wafers.
Processing apparatus for performing processes on semiconductor wafers to manufacture semiconductor integrated circuits are generally classified into two types. The first type is designed to process a number of wafers at a time. The second type is designed to process wafers one by one, at high speed. There is the trend that the second-type process apparatus is used in the case where the wafers are large and metal films are to be formed on the wafers. This is because the second-type process apparatus can form metal films of uniform thickness.
The second-type process apparatus comprises a process chamber, a table (susceptor), a heater (or a heating lamp), and a showerhead. The process chamber is shaped like, for example, a cylinder, and can be evacuated. The table is provided in the process chamber, for supporting one object to be processed (e.g., semiconductor wafers). The heater is located below the table, for heating the object placed on the table. The showerhead is arranged on the ceiling section of the process chamber and above the table, for applying a process gas to the single object mounted on the table.
In operation, the showerhead applies the process gas to the objects, while the heater is heating the object at a prescribed process temperature. A process is thereby performed on the object to form, for example, a film on the object.
FIGS. 8 and 9 show a conventional showerhead 2. As shown in FIG. 8, the showerhead 2 comprises a main body 6 and a cover 12. The main body 6 is connected to the ceiling section 4 of a process chamber and extends downward from the ceiling section 4. The main body 6 has an opening 6A in its lower end. The cover 12 has a number of gas-applying holes 10. The cover 12 is secured by bolts 14 to the lower end of the main body 6, closing the opening 6A. As seen from FIG. 9, the lower end of the main body 6 defines a large contact surface 16. It is at this surface 16 that the main body contacts the showerhead cover 12. The ceiling section 4 of the process chamber (i.e., the top of the main body 6) has a gas inlet port 8 for guiding the process gas into the showerhead 2.
The process gas is introduced through the gas inlet port 8 into the showerhead 6. The gas is then guided into the process chamber through the gas-applying holes 10. It is thereby applied into the process chamber in substantially uniform distribution. To apply the gas into the chamber more uniformly, a gas-dispersing plate 11 may be provided in the showerhead 2.
In order to manufacture semiconductor integrated circuits on the semiconductor wafer at a high yield, it is vitally important to heat the surface of the semiconductor wafer uniformly and to reduce particles on the surface of the semiconductor wafer. Many particles are formed, however, when the showerhead 2 is used to apply the process gas into the process chamber. As the temperature in the process chamber rises and falls, friction occurs between the main body 6 and cover 12 of the showerhead 2 at the contact surface 16 due to the difference in thermal expansion coefficient between the body 6 and the cover 12. Since the contact surface 16 is large as mentioned above, particles are inevitably formed in great quantities.
To decrease the friction between them, both the main body 6 and the cover 12 may be made of aluminum-based materials to have almost the same thermal expansion coefficient. Even in this case, friction between the body 6 and the cover 12 is unavoidable because the cover 12 thermally expands more than the main body 6. Namely, the cover 12, which is located near the heater, is heated to a higher temperature than the main body 6. The inventors hereof experimented with a conventional showerhead comprising a cover having a diameter of about 28 cm. The results of the experiment showed that friction had occurred over a distance of about 3 mm on the contact surface between the main body and cover of this showerhead.
To prevent friction at the contact surface 16 between the main body 6 and cover 12 of the showerhead 2 (FIG. 8), packing made of Teflon.RTM. is interposed between the main body 6 and the cover 12. Teflon has but low corrosion resistance; it cannot last sufficiently long to prevent forming of particles.
The wires and electrodes incorporated in semiconductor devices now have widths in the order of sub-micron, e.g., 0.2 to 0.5 .mu.m, since the devices have become smaller and yet their integration density has increased. It is now strongly demanded that measures be taken to reduce particles on the surface of a semiconductor wafer being processed.